BYR = 974   
USD = 840
EUR = 978
UAH = 980
GBP = 826
CHF = 756
JPY = 392

RUR = 810  # before denomination
RUB = 643  # after denomination. 1 RUB = 1000 * RUR   

_strcodes = dict((v, k) for k, v in locals().items() if len(k) == 3)
def currency2str(intcode):
    try:
        return _strcodes[intcode]
    except KeyError:
        raise 'Unknown currency `%s`' % intcode